HI

SXT stands for Solar X-ray Telescope. SXT was an X-ray telescope on the Japanese Yohkoh spacecraft. It was very very special because, by being above the Earth's atmosphere, it could image the X-ray flux from the Sun. It absolutely revolutionized our ideas about the activity going on in the solar corna.

To answer #3, SXT looks at the very hot part of the corona of the Sun. Only in regions where the corona is very hot does it emit X-rays.

Paulett